The present invention relates to shielding and electrical connection between boards in a dual printed circuit board assembly and, in particular, to a board to board RF shield with an integrated board to board connector/connector holder.
In an electronic device utilizing dual printed circuit boards, it is essential to shield various sections of the board from one another. For example, in a cellular phone, the logic section of the boards must be shielded from the RF section of the boards. The dual printed circuit boards must also be electrically coupled.
Many different shielding methods and connection methods exist, however, these methods have typically been made via two or more separate and distinct components. One method of shielding is a simple soldered can. In this method, a metal stamping is drawn and then soldered around the perimeter of the can to the board. A second method of shielding involves the use of a dual material board to board shield that separates the boards at a given distance as well as providing necessary shielding. In this method, a solid plastic core is overmolded with an electrically conductive elastomeric. When placed between the two boards, the elastomeric is compressed until the boards bottom out against the plastic core. Because the parts are molded, they can be of very complex shapes, typically of the board outline with dividers for the various sections on the boards. A third type of shielding between boards that has been used is a metallized injection molded plastic piece. Like the second method, this type of rigid construction also serves as a spacer between the boards. In some cases, small springs are clipped onto the molded piece between the mating surfaces to ensure proper contact and shielding.
Typically, the connection between the printed circuit boards is made with a separate connector assembly. Standard connector assemblies include male and female mating connectors, elastomeric connectors with separate holders and spring contact connectors. A standard surface mount connector is a two part component that depends on the manufacturing process to mate it properly. Misalignment can occur in both the X and Y plane and in the .theta. direction (.theta. is defined to be a rotation of the connector using its center as point of reference). A connector, whether surface mount or elastomeric, requires both boards to be aligned as accurately as possible. The elastomeric connectors and spring contact connectors have two alignment difficulties: first, shorting can result from the soldering mask rotating to cross two leads simultaneously, and second, noncontacts can occur when the leads do not touch the pad. Both of these problems are significant dangers and difficult to design around.
The prior art separate connector and shield arrangement disadvantageously takes up a significant amount of usable printed circuit board area. Moreover, with the conventional arrangements, the tolerance stack-up can be substantial, leading to problems with the final assembly. That is, if a pair of mating connectors is used in conjunction with a metallized plastic frame, which aligns the assembly, and the mated pair is soldered slightly out of line (but within tolerance), a large amount of stress could be placed on the connectors leading to field failures. Conversely, if the connectors are used to align the assembly, then the board edges may not align, and more space would be needed to house the dual board assembly, leading to a larger product. Still further, with larger tolerances required in the conventional assembly, the number of contacts in a given size connector is limited as the contacts must be sized sufficiently large enough to accommodate the tolerances.